Improvements to Deepwater Subsea Measurements RPSEA Program: Meter Alteration Effects From Fouling and Erosion

Abstract

Abstract Multiphase/wet gas flow meters used in deepwater subsea conditions are known tohave problems with scale from produced water and erosion from sand production. The objective of this RPSEA project is to evaluate the flow meter performancechanges produced by these meter altering mechanisms Multiphase/wet gas meter elements: Venturi, cone and wedge meters, werephysically tested and subjected to Computational Fluid Dynamics (CFD)simulations. The erosion testing was done with water-sand and air-sand on one size and onebeta ratio of each meter type. CFD simulations were used to extend the sizerange, the beta range and the fluid densities to cover the multiphase densityrange between air and water. Erosion results are presented that allows the user to estimate the possibilityor likelihood of wall penetration, the measurement error on a flow meter andthe effect of a flow meter on the erosion of a downstream bend. The scale deposition testing was done with brine of mostly sodium and calciumon one size and one beta ratio of each meter type. No attempt was made to useeither multiphase flow or realistic subsea conditions. Scale deposition is a highly complex and variable process that is difficult tomodel. For CFD to be able to estimate meter error it would have to predict thedistribution and thickness of scale in the meter. At present this is beyond thecapability of CFD. However, CFD simulations were run to assess how meters areaffected by scales that are sensitive to fluid scouring, pressure distribution, particle accretion and thermal effects. These CFD-based methods are sufficiently realistic to provide an insight intothe effects of scale. They are used to compare different meter designs andhence identify design features that may be desirable if scale formation is aconcern. 1. Introduction This RPSEA 07121–1301 [Ref. 1] project addresses gaps in the deployment and useof multiphase and wet gas meter technology in deepwater production systems. Inparticular the objective of this task is to understand the ways in whichproduction fluids affect subsea meters and thereby affect their meterresponses. It is known from field operations that meters can become fouled internally bydeposits of scale, or altered by erosion. At present these effects are not wellunderstood and the objective is to estimate their magnitude. Flow tests and computational fluid dynamic (CFD) analyses have been performedto evaluate the effects of alteration on Venturi, cone and wedge meters, byscale deposition and by sand erosion. The results are interpreted to give aclearer understanding of these meter alternation effects on subsea multi-phasemeter response.